libqtest: split qtest_spawn_qemu function

In order to create a function that allows testing of invalid command
lines, extract the parts of qtest_init_without_qmp_handshake that do
not require any successful set up of sockets.

Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

tests/qtest/libqtest.c

@@ -360,60 +360,25 @@ static pid_t qtest_create_process(char *cmd)
 }
 #endif /* _WIN32 */
 
-QTestState *qtest_init_without_qmp_handshake(const char *extra_args)
+static QTestState *G_GNUC_PRINTF(1, 2) qtest_spawn_qemu(const char *fmt, ...)
 {
-    QTestState *s;
-    int sock, qmpsock, i;
-    gchar *socket_path;
-    gchar *qmp_socket_path;
-    gchar *command;
-    const char *qemu_binary = qtest_qemu_binary();
+    va_list ap;
+    QTestState *s = g_new0(QTestState, 1);
     const char *trace = g_getenv("QTEST_TRACE");
     g_autofree char *tracearg = trace ?
         g_strdup_printf("-trace %s ", trace) : g_strdup("");
+    g_autoptr(GString) command = g_string_new("");
 
-    s = g_new(QTestState, 1);
-
-    socket_path = g_strdup_printf("%s/qtest-%d.sock",
-                                  g_get_tmp_dir(), getpid());
-    qmp_socket_path = g_strdup_printf("%s/qtest-%d.qmp",
-                                      g_get_tmp_dir(), getpid());
-
-    /* It's possible that if an earlier test run crashed it might
-     * have left a stale unix socket lying around. Delete any
-     * stale old socket to avoid spurious test failures with
-     * tests/libqtest.c:70:init_socket: assertion failed (ret != -1): (-1 != -1)
-     */
-    unlink(socket_path);
-    unlink(qmp_socket_path);
-
-    socket_init();
-    sock = init_socket(socket_path);
-    qmpsock = init_socket(qmp_socket_path);
-
-    qtest_client_set_rx_handler(s, qtest_client_socket_recv_line);
-    qtest_client_set_tx_handler(s, qtest_client_socket_send);
+    va_start(ap, fmt);
+    g_string_append_printf(command, CMD_EXEC "%s %s",
+                           qtest_qemu_binary(), tracearg);
+    g_string_append_vprintf(command, fmt, ap);
+    va_end(ap);
 
     qtest_add_abrt_handler(kill_qemu_hook_func, s);
 
-    command = g_strdup_printf(CMD_EXEC "%s %s"
-                              "-qtest unix:%s "
-                              "-qtest-log %s "
-                              "-chardev socket,path=%s,id=char0 "
-                              "-mon chardev=char0,mode=control "
-                              "-display none "
-                              "%s"
-                              " -accel qtest",
-                              qemu_binary, tracearg, socket_path,
-                              getenv("QTEST_LOG") ? DEV_STDERR : DEV_NULL,
-                              qmp_socket_path,
-                              extra_args ?: "");
-
-    g_test_message("starting QEMU: %s", command);
-
-    s->pending_events = NULL;
-    s->wstatus = 0;
-    s->expected_status = 0;
+    g_test_message("starting QEMU: %s", command->str);
+
 #ifndef _WIN32
     s->qemu_pid = fork();
     if (s->qemu_pid == 0) {
@@ -434,14 +399,56 @@ QTestState *qtest_init_without_qmp_handshake(const char *extra_args)
         if (!g_setenv("QEMU_AUDIO_DRV", "none", true)) {
             exit(1);
         }
-        execlp("/bin/sh", "sh", "-c", command, NULL);
+        execlp("/bin/sh", "sh", "-c", command->str, NULL);
         exit(1);
     }
 #else
-    s->qemu_pid = qtest_create_process(command);
+    s->qemu_pid = qtest_create_process(command->str);
 #endif /* _WIN32 */
 
-    g_free(command);
+    return s;
+}
+
+QTestState *qtest_init_without_qmp_handshake(const char *extra_args)
+{
+    QTestState *s;
+    int sock, qmpsock, i;
+    gchar *socket_path;
+    gchar *qmp_socket_path;
+
+    socket_path = g_strdup_printf("%s/qtest-%d.sock",
+                                  g_get_tmp_dir(), getpid());
+    qmp_socket_path = g_strdup_printf("%s/qtest-%d.qmp",
+                                      g_get_tmp_dir(), getpid());
+
+    /*
+     * It's possible that if an earlier test run crashed it might
+     * have left a stale unix socket lying around. Delete any
+     * stale old socket to avoid spurious test failures with
+     * tests/libqtest.c:70:init_socket: assertion failed (ret != -1): (-1 != -1)
+     */
+    unlink(socket_path);
+    unlink(qmp_socket_path);
+
+    socket_init();
+    sock = init_socket(socket_path);
+    qmpsock = init_socket(qmp_socket_path);
+
+    s = qtest_spawn_qemu("-qtest unix:%s "
+                         "-qtest-log %s "
+                         "-chardev socket,path=%s,id=char0 "
+                         "-mon chardev=char0,mode=control "
+                         "-display none "
+                         "%s"
+                         " -accel qtest",
+                         socket_path,
+                         getenv("QTEST_LOG") ? DEV_STDERR : DEV_NULL,
+                         qmp_socket_path,
+                         extra_args ?: "");
+
+    qtest_client_set_rx_handler(s, qtest_client_socket_recv_line);
+    qtest_client_set_tx_handler(s, qtest_client_socket_send);
+
     s->fd = socket_accept(sock);
     if (s->fd >= 0) {
         s->qmp_fd = socket_accept(qmpsock);